Protein-phenolic interactions in lentil and wheat crackers with onion skin phenolics: effects of processing and in vitro gastrointestinal digestion

This study aimed to evaluate the protein-phenolic interaction in functional crackers made of wheat/lentil flour with onion skin phenolics (onion skin powder: OSP, onion skin phenolic extract: OSE, or quercetin: Q) after in vitro gastrointestinal digestion. Phenolic/antioxidant recovery in crackers was lower with higher levels of phenolic addition. In vitro gastrointestinal digestion procedure was applied for crackers prepared/cooked with onion skin phenolics (functional crackers) or crackers consumed with onion skin phenolics (co-digestion). Functional crackers had similar nutritional attributes (p > 0.05), however they had lower L* values, and higher a* values. A higher concentration of OSP/OSE caused a decrease in the b* value while it was increased with the quercetin addition. Phenolic/antioxidant recovery in functional crackers was decreased by increasing the ratio of phenolic supplements. The amount of quercetin 7,4-diglucoside was lower than the theoretical value whereas the amount of quercetin was higher in functional crackers. The phenolic bioavailability index (BIP) of co-digested crackers was higher than that of functional crackers, whereas antioxidant bioavailability index (BIA) was mostly similar. Quercetin was only identified in functional wheat/lentil crackers with OSE. After digestion (1) TCA-precipitated peptides of the wheat crackers could not be identified, whereas that of co-digested lentil crackers was more abundant, (2) level of free amino groups of co-digested/functional crackers were lower than the control except for the co-digested sample of lentil cracker with quercetin.

Automated summary

This study aimed to evaluate the protein-phenolic interaction in functional crackers made with wheat/lentil flour and onion skin phenolics. The recovery of phenolics and antioxidants in the crackers decreased with a higher addition of phenolics. The nutritional attributes of the functional crackers were similar, but they had lower L* values and higher a* values. The phenolic/antioxidant recovery in the functional crackers decreased with an increased ratio of phenolic supplements. The bioavailability index of phenolics was higher in co-digested crackers compared to functional crackers, while the bioavailability index of antioxidants was mostly similar. Quercetin was only identified in functional wheat/lentil crackers with onion skin phenolic extract. After digestion, the peptides of wheat crackers could not be identified, while the level of free amino groups in co-digested/functional crackers was lower than the control group.